The invention related to the holding of a cutting tool, in particular a knife such as a bottom knife, which has at least two cutting edges. The bottom knife is coactable with at least one upper knife. At least one of the knives can be moved in such a manner that the upper knife can coact optionally with several cutting edges of the bottom knife. The bottom knife is rotatably mounted on a support shaft and is movable therealong to a desired setting position. The shaft is fixedly mounted on the machine frame and extends at right angles to the direction of formation of the web to be cut, the shaft extending through the bottom knife.
Devices of the aforementioned type having circular lower and upper knives or cutters are used in suitable machines to cut web-shaped materials. Usually a relatively wide web is cut with longitudinal cuts into relatively narrower individual webs if, for example, a roll of relatively wide web-shaped material is unwound and is then rewound into several rolls with respectively narrower width. To this end, socalled circular knives are used, where these cutting devices frequently consist of socalled upper and lower knives. The lower knives used in this case often comprise socalled cutting boxes, i.e. such lower knives, which have several cutting edges that are arranged coaxially to one another and with which an upper knife is coactable optionally with one of these cutting edges. The web-like material to be cut usually comprises paper, fabric, foils, metals or Plastics. However, other materials such as cardbord are also conceivable.
When cutting paper, fabric foil, metals or the like longitudinally, a distinction is made between the socalled straight cut and the socalled looped cut. During the straight cut, the web to be cut into individual strips travels through approximately tangentially between at least one upper and at least one lower knife, so that in this manner at least two strips are produced from one web. However, not only one pair of knives but also several pairs of knives, i.e. lower and upper knives respectively, can coact with one another, in order to cut a relatively wide web into a plurality of relatively narrow webs. The final processor of the web to be cut often desires webs of different width; for which reason there exists the demand to cut a relatively wide web during one production process, for example, into relatively wide webs, and during another, possibly subsequent production process into relatively narrow webs. As a rule these cut webs are wound into rolls, in order to be able, for example, to send these webs in an easy and convenient manner to the final processor. The changing demands of the final processor means for the person who has to divide a relatively wide web into individual webs that the device available to him must be correspondingly changed over; this process is commonly called "positioning". During a socalled straight cut it is relatively simple to position the lower and upper knife, since the web does not press against one of the two knives and thus impede its mobility. With the socalled looped cut, however, it is much more difficult to move the knife, i.e. as a rule the lower knife, around which the web is wrapped, since owing to the stress prevailing by necessity in the web for the purpose of Processing, the web presses against the lower knife. The lower knife is thus restricted in its mobility, for which reason it is mandatory especially in this case to provide that the lower knife moves with ease of motion when the position of this lower knife is to be changed.
German patent 10 38 902 discloses a known device in which several lower knives, i.e. socalled cutting boxes, are lined up in the axial direction side by side on a cylinder or a roller body serving as the guide for the cutting boxes. The cylinder can be rotated in a machine frame, the consequence of which is that, for example, at high speeds the bearings of the cylinder oscillate; these oscillations are transferred to the knives mounted on the cylinder and can lead to undesired cutting results, i.e., a poor cut, of the web to be cut. The lower knives of this prior patent can be moved by negligible amounts in the axial direction, but only when the lower knives are moved by hand with respect to the guide supporting them. Since the lower knives are relatively large and thus heavy, it is difficult and time consuming to bring these lower knives to an accurately predetermined position, a process that is also rendered more difficult by the frictional forces that are generated. In this manner it becomes difficult and time-consuming to align the lower and upper knives in such a manner against one another with this prior art device that they interact well and yield a predetermined width of the strip to be cut.
In the device according to published German application 36 04 701 the bottom and upper knives are mounted in separate carriages, the carriages being movable on separate guides. This construction is quite complicated and requires a lot of space. Due to the great distances between its components, it is also sensitive to oscillations.
The same also applies correspondingly to the device of U.S. Pat. No. 4,233,889 in which the knives are also mounted in a revolver, whose mounting also does not provide for a stable and precision balanced structure.
A cutting device is also disclosed in German Patent No. 22 50 125 wherein tension mechanisms are assigned to each knife in order to bring such knife to the desired position. However, this prior art device also requires a lot of space and is thus expensive and sensitive to oscillations.
In addition, U.S. Pat. No. 4,759,249 discloses a device which makes it possible to easily move the knives with respect to the shaft supporting them. However, this shaft is mounted in a machine frame, i.e., with bearings that are far apart from one another.
U.S. Pat. No. 4,646,603 discloses another device which makes it possible to easily move the knives with respect to the shaft supporting them. However, in this case the invention involves a mechanical action which requires grooves machined into the supporting shaft. These grooves can have a negative impact on the stability of the supporting device or require larger dimensions to obtain identical stability.
A mounting for a socalled upper knife is disclosed in U.S. Pat. No. 4,143,572. However, such upper knives are very easily compared to bottom knives, which contain at least two usable cutting edges, thus are socalled cutting boxes. Such cutting boxes are quite heavy, especially when they have a relatively large diameter. With respect to the mobility of the upper and lower knives the problem is totally different, so that no suggestion regarding how to move the lower knives efficiently can be derived from the patent.
A device to fix in position the knives on a shaft supporting them is disclosed in U.S. Patent No. 4,189,967. However, here the problem is to produce a tight seat, but it does not involve the problem of being able to move such knives rapidly and simply.